The present invention relates generally to monitoring and/or controlling an electric cooktop, and, more particularly, to a system for generating control signals responsive to properties of a cooking utensil detected by using a parameter indicative of the temperature of the cooktop surface.
Recently, standard porcelain enamel cooktop surfaces of domestic ranges have been replaced by smooth, continuous-surface, high-resistivity cooktops located above one or more heat sources, such as electrical heating elements or gas burners. The smooth, continuous-surface cooktops are easier to clean because they do not have seams or recesses in which debris can accumulate. The continuous cooktop surface also prevents spillovers from coming into contact with the heating elements or burners. Exemplary cooktops comprise glass-ceramic material because of its low coefficient of thermal expansion and smooth top surface that presents a pleasing appearance.
Devices are known for detecting the presence of a utensil on a cooking appliance, such as those dependent on contact with the cooking utensil disposed on an electric heating element or on the utensil support of a gas burner. Such contact-based systems, however, have not proven to be feasible for continuous-surface cooktops, and especially glass-ceramic cooktops due to the difficulties of placing contact sensors thereon. Cooking utensil contact sensors generally disrupt the continuous cooktop appearance, weaken the structural rigidity of the cooktop, and increase manufacturing costs. Also, such contact-based systems are not inherently reliable on smooth-surface cooktops because cooking utensils with warped or uneven bottoms may exert varying forces on the contact sensors and give a false contact indication.
None of the known arrangements include an algorithm that compares a combination of signals indicative of temperature of a cooking utensil and/or the solid cooktop surface and power applied to one or more heat sources used for cooking to determine the physical properties of the cooking utensil. In addition, no known arrangement uses an algorithm that learns with experience.
Accordingly, it is desirable to provide a system for detecting cooking utensil characteristics or utensil-related, through-the-cooktop-surface properties, such detection being independent of a cooking utensil""s composition, flatness of bottom, or weight. Such a desirable system should perform such detection with an evolutionary algorithm that processes temperature and power signals. It is further desirable that such a system generate energy source control signals based on detecting temperature indicative signals through the glass-ceramic cooktop, and processing such signals together with power indicative signals, to determine the presence/absence, removal/placement, warpage, size, temperature, or the contents or load of a cooking utensil on the cooktop.
The system of the present invention is arranged and configured for automatically controlling the temperature of the cooking surface of a cooking surface of a solid-surface cooktop, and, consequently, the temperature of the cooking utensil on the cooking surface, by detecting cooking utensil-related properties through the solid-surface cooktop. The cooking utensil-related properties include presence/absence, removal/placement, and other physical properties such as utensil type, size, warpage, temperature, and load size.
The approaches disclosed herein are primarily based on monitoring the heat transfer characteristics from the energy source to the cooktop and the utensil to infer the utensil properties. This is achieved by sensing or inferring a parameter indicative of the temperature of a monitored area that includes at least a portion of a cooktop or of the cooking utensil placed on the upper surface of a cooktop. The temperature parameter sensor includes at least one detector, and additional sensors may be used for sensing other parameters for improved detection capability. A second parameter indicative of power applied to at least one controllable energy source (e.g., comprising electric or gas heating elements or induction heating sources) is sensed and a power signal is developed for subsequent processing, together with the parameter indicative of temperature.
The at least one controllable energy source is arranged to heat the contents of a cooking utensil placed on the cooktop. The utensil property detecting system may include a monitoring system for monitoring the properties of the cooking utensil, or it may include a control system for controlling the energy source based on the detected utensil properties, or both.
In one embodiment, the sensor is arranged to detect the temperature of the cooktop directly in contact with the cooking utensil. The characteristics of the temperature changes of the cooktop are dependent upon the type, size and other characteristics of the cooking utensil, as well as the power level of the energy source and the temperature of the cooktop. The impact of various types, sizes and condition of a cooking utensil on the cooktop on temperature is determined experimentally and stored as data within a processor, which receives the signal indicative of temperature from the sensor. The processor selects a power level, processes the received signal indicative of temperature, and compares the result to the stored data, thereby determining the type, size and other characteristics of the cooking utensil. Based on the detected signals, the processor employs an algorithm to provide signals indicative of the status of the cooking utensil. In a separate embodiment, the detected signals are used by the processor to provide control signals to the energy source in order to optimally support the particular cooking utensil or cooking mode set by the user of the cooktop.
In a separate embodiment, heat transfer models based on predetermined physical characteristics of utensils and power and heat flux properties are used for estimation or inferral of utensil temperature.
In all embodiments of the present invention, an algorithm employed by the processor processes a combination of signals including the signal indicative of temperature related to the solid cooktop surface and/or the cooking utensil located on the surface, and also a signal indicative of the power going to one or more heat sources used for cooking, to determine the physical properties of the cooking utensil. The algorithm can be an evolutionary algorithm that updates comparison rules in accordance with calculated differences between detector signal levels and known signal patterns.